1. Field of the Invention
The present invention relates to a multi-port apparatus (device) used to control a plurality of apparatuses through serial communication ports, and more particularly, to a serial multi-port communication method for communications with a plurality of apparatuses through two serial communication ports mounted in a computer, an apparatus suitable to the method, a method for controlling this apparatus and a recording medium suitable to this control method.
2. Description of the Related Art
As is well-known, an IBM compatible computer provides two standard serial communication ports (COM1, COM2), but in some applications, more ports may be needed. In order to satisfy this demand, multi-port devices have been developed and these multi-port devices usually support 6-8 universal asynchronous receiver-transmitter (UART) ports.
The related art regarding these multi-port devices is broadly explained in ‘SERIAL COMMUNICATIONS Developer's Guide 2nd Edition’, IDG BOOK, pp.25-26, and also is disclosed in U.S. Pat. No. 4,866,667 (laid open Sep. 12, 1989), U.S. Pat. No. 4,868,784, and JP 2002-215555.
FIG. 1 is a block diagram showing the structure of a related art multi-port board. The apparatus shown in FIG. 1 is mounted into an industry standard architecture (ISA) slot, or a peripheral component interconnect (PCI) slot of a computer, and is used after being connected to a PCI/ISA bus 102.
In the apparatus shown in FIG. 1, a UART controller 104 which converts parallel data into a serial signal is installed in each port (ports 1 through 4) for providing serial communications. With the UART controllers 104, the apparatus of FIG. 1 comprises an interrupt management unit 106 which arbitrates interrupts from these UART controllers 104, and a data switching unit 108 which enables to read data from and write data in the registers of the UART controllers selectively.
Each UART controller 104 independently generates an interrupt signal for requesting service. Once an interrupt is generated, the interrupt management unit 106 sends this interrupt to a central processing unit (CPU, not shown) through the PCI/ISA bus without distinguishing the source UART controller 104 of the interrupt. In the CPU of the computer, one interrupt request (IRQ) is allocated to the multi-port board shown in FIG. 1 (not to each of the ports), and driver software installed in the computer distinguishes which port requests interrupt service.
If an interrupt is generated, the interrupt service routine of the driver software confirms the content of a status register installed in each UART controller 104, by switching each UART controller 104 with the data switching unit 108, and provides data transmission or reception service for a port, if based upon the port status register, that the port needs the data transmission/reception service.
That is, the interrupt service routine reads data from a Received Holding register installed in a UART controller 104 whose Data Received flag is set, because the UART controller 104 received data through an RX signal line, and for a UART controller 104 which finishes data output to a TX signal line, loads data to be transmitted next on a Transmit Holding register installed in the UART controller 104. If there is not other UART controller 104 that needs service, the interrupt service routine is finished.
Since this related art multi-port device is usually constructed to have a shape to be inserted into an ISA slot or a PCI slot of a computer, the related art multi-port device has an inconvenience of requiring opening the case of a personal computer (PC) when detaching the device from the ISA/PCI slot of the computer, for example, for maintenance, for adding more multi-port slot cards, removing multi-port slot cards, etc., and needs a complex hardware design to comply with ISA/PCI bus standards of the computer. In addition, when it is designed to support a plurality of ports, due to the narrow inside space of a computer, the number of ports that can be accommodated is limited, such that it is inevitable to separately provide another slot mounting board for more external ports.
Furthermore, the related art multi-port device needs a separate interrupt management unit 106 for arbitrating interrupts generated in ports, and whenever a port is added, a UART controller should also be added, such that cost of manufacturing increases.
Furthermore, the related art multi-port device needs installation of a separate driver software for each provided port for controlling the devices via the ports and an engineer who develops an application program for controlling a plurality of apparatuses by using the software should have a thorough knowledge on the method of using the driver software, which causes inconvenience in distribution and usage of the device.